I have an Xbox, but the first game I got all the achievements for was Assassin's Creed 2. I loved that game, it was all I'd play for ages.
I wanted to do the same with all the other games, but as Brotherhood and Revelations require multiplayer achievements, I doubt I'll ever actually do so.
Saying that, the first one I could get all of them for... But the prospect of searching for all those flags just seems too much of a daunting task.
However, I later have managed to get the twenty for Minecraft (come here little pig, just need to put this saddle on you... And then kill you...).